1. Field of the Invention
The present invention relates to an image recording method and apparatus and, more particularly, to an image recording method and apparatus which can perform a low-power, high-speed print operation using a recording head having a plurality of recording elements.
2. Description of the Related Art
As conventional serial printers, thermal transfer printers, ink-jet printers, and the like are available. Such an apparatus has a plurality of recording element arrays. These recording element arrays are arranged parallel to the convey direction of a recording sheet. A print operation for one recording sheet is completed by the fact that the recording element arrays sequentially scan in a direction perpendicular to the convey direction.
Recently, in order to achieve high print speed, the number of recording elements included in the above recording element arrays (the length of the recording head) has greatly increased.
This tendency toward the elongation of the recording head raises problems of increases in the capacity, size, and cost of a power supply, and the like.
With regard to a power supply for driving a printer, compact, high-efficiency, high-power switching power supplies have been widely used with advances in switching regulator techniques. Such power supplies, however, are more expensive than power adaptors of the conventional transformer scheme. Note that these power supplies can be classified into the type of power supplies which are incorporated in printers and adaptor-type of power supplies which are independent of printers.
The demand for the above power supply to have higher power is based on an increase in power required for a recording operation with the elongation of a recording head. More specifically, as the number of recording elements increases, the number of recording elements to be driven per unit time increases. When, for example, an image having an average density Z [%] is to be recorded by an ink-jet recording head having n nozzles with a discharge frequency f [Hz] and a drive pulse width T [sec], a required power Pn is given by: EQU Pn=(I.multidot.V.multidot.n).multidot.(T.multidot.f).multidot.Z (1)
where I is the peak value of a rectangular pulse current flowing in each recording element, and V is the power supply voltage value.
As is apparent from equation (1), according to an increase in the number of nozzles n, the discharge frequency f, and/or the average density Z, the power Pn increases.
In order to realize a high-speed print operation by increasing the number of nozzles with lower power, the value of each parameter must be decreased. However, the parameter Z is a value unique to an image, and a decrease in the value of the parameter f leads to a decrease in print speed. Therefore, it is not preferable that the values of these parameter be decreased.